1. Field of the Invention
This invention relates to a buckle device which is used in a seat belt or the like.
2. Description of the Related Art
A buckle device used in a seat belt is equipped with a locking member which is to be engaged with a tongue plate for the purpose of locking the same. This locking member is designed to be displaceable in such a way as to release the lock of the tongue plate.
In some cases, the lock of the tongue plate in such a buckle device is released by means of a lever member using its middle section as the fulcrum.
FIG. 5 shows the mechanism of a buckle device of this type. In the example shown, a lock plate 10 serving as the locking member can be displaced in the vertical direction. When moved downwards, it is inserted into a through-hole 14 provided in a tongue plate 12, thereby locking the tongue plate 12 with respect to this buckle device. A lever 16 serving as the lever member is rotatably mounted, using its middle section as the fulcrum. When a push button 18 provided at that end of the lever 16 which is on the opposite side of the lock plate 10 is depressed downwards, that end of the lever 16 at which the lock plate 10 is provided is moved upwards to extract the lock plate 10 from the through-hole 14, thereby releasing the lock of the tongue plate 12.
In the above lever 16, the lever ratio K is determined as: K=L1/L2&gt;1 so that the requisite force for operating the push button 18 can be relatively small. Accordingly, when the stroke for moving the lock plate 10 from the lock position to the release position is represented as S1, the stroke S2 for the push button 18 is to be represented as S1.times.K. Thus, the buckle device is required to have a relatively large thickness before the stroke S2 can be ensured, which constitutes an obstacle to miniaturization of the device.
Diminishing the lever ratio K might naturally allow the stroke K to be reduced, and consequently, the device to be miniaturized. However, this results in the requisite force for operating the push button 18 being augmented, which makes the device hard to operate.